Copolymers of tetrafluoroethylene (TFE) and a co-monomer according to the formula: FSO2—CF2—CF2—O—CF(CF3)—CF2—O—CF═CF2 are known and sold in sulfonic acid form, i.e., with the FSO2— end group hydrolyzed to HSO3—, under the trade name Nafion® by DuPont Chemical Company, Wilmington, Del. Nafion® is commonly used in making polymer electrolyte membranes for use in fuel cells.
Copolymers of tetrafluoroethylene (TFE) and a co-monomer according to the formula: FSO2—CF2—CF2—O—CF═CF2 are known and used in sulfonic acid form, i.e., with the FSO2— end group hydrolyzed to HSO3—, in making polymer electrolyte membranes for use in fuel cells. Moore and Martin, Morphology and Chemical Properties of the Dow Perfluorosulfonate Ionomers, Macromolecules, vol. 22, pp. 3594-3599 (1989) discloses Tg values for samples of this polymer having various equivalent weights, measured by differential scanning calorimetry (DSC). That article reports the Tg measurements repeated in Table I:
TABLE IEquivalent WeightTg 635177° C. 803179° C. 909165° C.1076158° C.1269158° C.
U.S. patent application Ser. No. 10/325,278, filed Dec. 19, 2002, the disclosure of which is incorporated herein by reference, discloses a polymer electrolyte membrane having a thickness of 90 microns or less and comprising a polymer, said polymer comprising a highly fluorinated backbone and recurring pendant groups according to the formula:YOSO2—CF2—CF2—CF2—CF2—O—[polymer backbone]where Y is H+ or a monovalent cation such as an alkali metal cation. Typically, the membrane is a cast membrane. Typically, the polymer has a hydration product of greater than 22,000. Typically, the polymer has an equivalent weight of 800-1200.
U.S. Pat. Nos. 4,358,545 and 4,417,969 purportedly disclose polymers and ion exchange membranes thereof having a hydration product of less than about 22,000 and equivalent weight of 800-1500, which have a substantially fluorinated backbone and pendant groups according to the formula: YSO3—(CFRf)a(CFR′f)b—O—backbone, where Y is hydrogen or an alkali metal, Rf and R′f are halogen or substantially fluorinated alkyl groups, a is 0-3, b is 0-3, and a+b is at least 1.
Kokai Patent Application No. SHO 58-93728 purportedly discloses at Example 3 the copolymerization of TFE and FSO2—CF2—CF2—CF2—CF2—O—CF═CF2. The resulting polymer is extrusion molded to produce a film with a thickness of 150 microns and hydrolyzed, the resulting membrane having an equivalent weight of 990. This film was further treated so as to convert sulfonic acid groups to carboxylic acid groups in a thin surface layer of one side of the membrane.
Zaluski and Xu, Blends of Nafion and Dow Perfluorosulfonated Ionomer Membranes, Macromolecules, vol. 27, pp. 6750-6754 (1994) purportedly describes membranes comprising blends of Nafion® and Dow perfluorosulfonated ionomers. No Tg is reported for the blend. The membranes were cast onto slides and heated to 130° C.